bahar qarabaqi azar 19 th, 1386. fc inferencing initial information about the problem being asserted...
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Bahar QarabaqiAzar 19th, 1386
FC InferencingInitial information about the problem being
asserted into working memory.DatabaseSensorsUser
FC Inferencing (cont.)1. Scan the rules looking for ones whose
premises match the contents of the working memory.
2. Fire the rule which was found.3. Place its conclusion in the working memory.4. Until no additional rule fire, go to 1.
2. Fire the rule which was found… May locate several rules must decide Recognize-Resolve-Act cycle:
1. Scan the rules looking for ones whose premises match the contents of the working memory.
1’. Choose one rule to fire.2. Fire the rule which was found.3. Place its conclusion in the working memory.4. Until no additional rule fires, go to 1.
1’. Choose one rule to fire…Conflict resolutionSimplest:
Rules are examined in orderThe first rule is chosen
A common strategy:Each rule has a number which indicates its
priorityThe rule with the highest priority is chosen
…
Example 1:Pumping Station Diagnostic System
Block:a pump & a motorIncrease the water
pressure by 50 psiSensors:
line pressuremotor currents
Nominal values are available
An Event-Driven ES
Event-Driven vs. Conventional ESConventional ES
interacts with a user.Event-Driven ES
only becomes active when some special event occurs
Example 1–Problem Solving ApproachProblem solving strategy:
Fault detectionFault isolationFault diagnosis
Most ESs follow this sequence.Some also include fault response.Knowledge base is divided into various
sections
Example 1 – Fault Detection1. Numeric readings qualitative
descriptions2. Any fault low pressure 3. Faults propagate
Result: only need to monitor the final line pressure
Example 1 – Fault Detection (cont.)
Example 1 – Fault Detection (cont.)
Example 1 – Fault Isolation Why isolation?
By first identifying the faulty block, the system can concentrate its diagnostic effort on this single block.
Comparison of the block’s input pressure with its output pressure
Example 1 – Fault Diagnosis Which component is at fault?
Motor: low current Pump: no change in pressure Line: the block’s input pressure is less than
its output pressure
Example 1 – Fault Diagnosis (cont.)
Example 1 – Review Partitioned Rules:
Improve readability enhance maintenance
Intermediate Findings: Reports: what was observed and what the
system would look into next Intelligent Safety Net:
If the system is unable to determine the faulted component, knowing the general source may be valuable.
Example 1 – Review (cont.) Numeric Relationships:
49.99 is a low pressure! Solution: fuzzy logic
Specific Rules: Similar but separate rules for similar objects Solution: Example 2!
specific objects as variables
Example 2:Generalized Pumping Station Diagnostic System
Information about the structural relationship between components
Example 2 – Problem Solving ApproachProblem solving strategy:
General Fault DetectionGeneral Fault IsolationGeneral Fault DiagnosisGeneral Fault Response
Example 2 – General Fault Detection Fault Detection Heuristic:
If any line pressure drops below its nominal pressure, then you have a fault condition.
Used in RULE 1S
Example 2 – General Fault Detection
Example 2 – General Fault Isolation Fault Isolation Heuristic:
If you notice that a block’s input pressure is normal, but its output pressure is low, then the block may be faulty.
Example 2 – General Fault Diagnosis Which component is at fault?
Motor Problem Heuristic: A motor with a low current is suspect.
Pump Problem Heuristic: Pump problems usually result in no pressure
changes across the pump. Line Problem Heuristic:
When you see no problems with a block’s motor, but there is some increase in pressure across the block, there may be a leak in the output line.
Example 2 – General Fault Diagnosis
Example 2 – General Fault Response Purpose: replace the faulty component Only when the user has granted permission
Example 2 – Review Streamlining Rules:
A small number of general rules containing variables instead of a large set of rules.
Ease of Expansion: If additional objects added, only need to
assert their initial configuration information Stopping the System:
1. A common technique, but not the best: on their own
2. Force the system to stop
Example 2 – Review (cont.) Requesting Information:
1. Startup Rule:IF Get initial informationThen ASK …AND ASK …
2. When certain events occur1. As a part of a rule (our example)2. Demon Rule: the highest priority
IF ?Line pressure-status lowTHEN ASK shut down
Example 3:Train-Loading Expert System
Problem:Pack the passengers of various weights into a
series of train cars.Pack the persons by decreasing weight.Not exceed maximum weight capacity of train
car.Maximize the number of persons per train car
thus minimizing the number of cars needed.
ESs for Design ApplicationsDesign: configuring objects under a set of
constraintsConstraint:
1. Requirements: meet the design goal FC required: BC does not work in design
applications.
2. Methods: order of the steps1. Control Rules required:
IF <step> AND <heuristic> THEN <action>
2. Rule Ordering: simple to design, difficult to maintain3. Rule Priorities: difficult to maintain
Example 3–Problem Solving Approach
Example 3–Problem Solving Approach
Example 3–Problem Solving Approach
Example 3– Review Designed to Spec:
Final design met the stated specifications! Rules in Design Systems:
IF <step> AND <heuristic> THEN <action>